Simplify VisitOperator for VisitConstOperator

[alexcrichton]

Don't generate a format!-per-opcode but instead delegate to a single helper method.

[Robbepop]

@alexcrichton I just ran cargo bloat on the most recent Wasmi v0.40 version that uses the new wasmparser v0.221 and const-expr validator still is marked as bloated:

    Analyzing target/release/wasmi_cli

 File  .text    Size        Crate Name
 1.2%   2.1% 49.0KiB         wast <wast::core::expr::Instruction as wast::parser::Parse>::parse::{{closure}}
 1.0%   1.7% 38.8KiB   wasmparser wasmparser::validator::core::ModuleState::check_const_expr
 0.9%   1.5% 35.6KiB wasm_encoder <wasm_encoder::core::code::Instruction as wasm_encoder::Encode>::encode
 0.8%   1.4% 31.6KiB    wasmi_ir? <wasmi_ir::enum::Instruction as core::fmt::Debug>::fmt
 0.7%   1.3% 29.3KiB        wasmi wasmi::engine::translator::driver::FuncTranslationDriver<T>::translate_operators
 0.6%   1.1% 26.3KiB        wasmi wasmi::engine::executor::instrs::execute_instrs
 0.5%   1.0% 22.3KiB         wast wast::core::binary::encode
 0.5%   1.0% 22.2KiB    wasmi_cli wasmi_cli::context::Context::new
 0.5%   0.9% 21.5KiB        wasmi wasmi::module::parser::buffered::<impl wasmi::module::parser::ModuleParser>::parse_buffered_impl
 0.4%   0.7% 16.0KiB        wasmi wasmi::engine::translator::driver::FuncTranslationDriver<T>::translate_operators
 0.4%   0.7% 16.0KiB   wasmi_cli? <wasmi_cli::args::Args as clap_builder::derive::Args>::augment_args
 0.4%   0.7% 15.4KiB clap_builder clap_builder::derive::Parser::parse
 0.4%   0.7% 15.4KiB clap_builder clap_builder::parser::parser::Parser::get_matches_with
 0.4%   0.7% 15.3KiB          wat wat::Parser::_parse_str
 0.3%   0.6% 13.8KiB clap_builder clap_builder::parser::validator::Validator::validate
 0.3%   0.6% 13.2KiB         wast <wast::core::custom::Custom as wast::parser::Parse>::parse
 0.3%   0.5% 12.5KiB        wasmi wasmi::engine::translator::driver::FuncTranslationDriver<T>::translate_operators
 0.3%   0.5% 12.2KiB  wasmparser? <wasmparser::readers::core::operators::Operator as core::fmt::Debug>::fmt
 0.3%   0.5% 11.3KiB         wast wast::core::module::ModuleField::parse_remaining
 0.2%   0.4% 10.2KiB        wasmi wasmi::engine::translator::driver::FuncTranslationDriver<T>::translate_operators
46.7%  81.8%  1.9MiB              And 5298 smaller methods. Use -n N to show more.
57.1% 100.0%  2.3MiB              .text section size, the file size is 4.0MiB

Though it could be that multiple different wasmparser versions are at play.
However, cargo tree -p wasmi_cli | grep 'wasmparser' reveals only one:

│   └── wasmparser v0.221.0

[alexcrichton]

Ah yeah I'd probably try to get the old wasmparser pruned first to confirm it's not coming from there. If it's still here though happy to help dig in